An artificial knee that has first and second knee components connected together for rotation between a first, upright position and a second position where one knee component is positioned at an angle to the other, an alignment mechanism associated with the first and second knee components to assure rotation in a vertical plane from the first position to the second position, and a biasing member. One knee component includes an extension member located in a central location, while the other includes a centrally located slot that receives the extension member and allows rotation only in a vertical plane. The biasing member normally holds the knee components in the first position, such that rotation of the first knee component away from the second knee component stretches or elongates the biasing member to provide a force that urges the knee components to move back to the first position.
